The present invention relates to material deposition, generally, and more specifically to the patterned deposition of materials on a surface through the use of material suspended in a compressed state and ejected in a thin stream onto the surface.
Systems for the deposition of material upon surfaces are fundamental to the construction of integrated circuits and optical systems. Integrated circuit construction is usually based upon photo-lithographic techniques wherein flat surfaces (such as wafers) are exposed to ultra-violet light, sputtering, or chemical vapors through a mask. Other techniques rely on the use of charged particle beams for implanting materials at specific locations. The beams may be steered through the use of electromagnetic fields. Materials may be deposited upon optical elements through, for example liquid coating and vapor deposition. Structures on optical surfaces may be created, for example by etching or mechanical cutting and polishing.
Processes that enable patterned deposition of materials onto a substrate have a number of applications, especially in the electronic microcircuit industry. Micro-fabrication of electronic circuits relies on the ability to create multi-layer patterns of numerous functional materials, with varying electrical properties. The technologies used for creating these multi-layer patterns may be additive, subtractive or a combination of the two: Additive technologies deposit the functional material on the substrate in the desired pattern; i.e., the pattern is generated directly on the substrate during the deposition/layering process, while subtractive processes first create a continuous layer of the functional material on the substrate and the desired pattern is then subsequently created by the selective removal of functional material from the deposited layer; i.e., the pattern is created subsequent to the deposition/layering process. A detailed description of various patterned deposition/layering processes used in the microfabrication industry may be found in xe2x80x9cThe Physics of Micro/Nano-Fabrication,xe2x80x9d Ivon Brodie and Julius J. Murray, Plenum Press, NY, 1992.
Traditional microfabrication processes utilize either or both the additive and subtractive processes depending upon the specific application, and are generally carried out in a high vacuum (low pressure) environment. The high vacuum process generally involves the evaporation of functional material by beating or by ion bombardment followed by deposition on the substrate by condensation or by a chemical reaction. A feature common to all these processes is that the functional material to be deposited has to be thermally stable or has to have a thermally stable precursor that can generate the function material on the substrate by a chemical reaction. These processes are not useful in generating patterned layers of thermally unstable materials.
It is common in the art to use a mask technique for patterned deposition. Typically, the mask employed for patterning on a planar substrate surface is a photo-resist material. However, when the surface is non-planar, difficulties can be encountered in depositing and cleaning off the photo-resist material, necessitating the use of shadow masks or stencils. For example, Dunkleberger in U.S. Pat. No. 4,218,532 describes a method for patterned deposition of thin films of metals such as lead alloys by vacuum evaporation onto a substrate through openings in a mask that is fabricated with a predetermined pattern. There is a problem with this technology however, in that it cannot be used for the patterned deposition of thermally unstable materials since these are not suitable for vacuum evaporation. Staples in U.S. Pat. No. 4,013,502 describes a process for high resolution pattern replication using stencils, where the stencil is used as a mask in molecular beam deposition of thin films of materials onto a substrate through the openings in the stencil, where the molecular beam source is a E-beam evaporator. There is a problem with this technology also in that it cannot be used for patterned deposition of thermally unstable materials that are not suitable for evaporation using an E-beam. Moreover, use of photolithographic techniques renders the use of non-planar substrates problematic since maintaining a high-resolution focus is difficult.
Patterned deposition of thermally unstable materials on substrates may be achieved by liquid phase processes such as electroplating, electrophoresis, sedimentation, or spin coating but these processes are system specific. For example, in the case of electroplating, it is necessary that an electrochemically active solution of the functional material precursor is available. In the case of sedimentation and spin coating, a stable colloidal dispersion is necessary. In the case of electrophoresis, it is also necessary that the stable colloidal dispersion be charged. Micro-fabrication of multi-layer structures usually requires multiple stages, necessitating the complete removal of residual liquids/solvents at the end of every stage, which can be very energy, time, and cost intensive. Further, many of these liquid-based processes require the use of non-aqueous liquids/solvents, which are hazardous to health and the disposal of which can be prohibitively expensive. For example, Doss et al. in U.S. Pat. No. 5,545,307 disclose a process for patterned electroplating of metals onto a substrate through a mask. This technology has two major problems in that it is only applicable to materials that have electrochemically active precursors and it uses an aqueous electroplating bath for the process, requiring that the coated substrate is cleaned and dried at the end of the coating process.
To eliminate the need for potentially harmful solvents that need drying, it is possible to use environmental and health-benign supercritical or dense-phase fluids such as carbon dioxide as solvents. For example, Murthy et al. in U.S. Pat. No. 4,737,384 disclose a process for depositing thin films of materials that are soluble in supercritical fluids onto a substrate. The process of this invention comprises of the steps of: exposing a substrate at supercritical temperatures and pressures to a solution comprising of a metal or polymer dissolved in water or a non-polar organic solvent, said metal or polymer being substantially insoluble in said solvent under sub-critical conditions and being substantially soluble in said solvent under supercritical conditions; and reducing the pressure, or temperature and pressure to sub-critical values, thereby depositing a thin coating of said metal or polymer on said substrate. There is a problem with this technology in that it only applies to materials that can be dissolved in supercritical fluids, severely limiting the choice of materials that can be deposited on a substrate using this technology. Further, this patent does not teach a process for the patterned deposition of functional materials. Smith in U.S. Pat. Nos. 4,582,731 and 4,734,227 also discloses processes for the creation of solid films by dissolving a solid material into supercritical fluid solution at an elevated pressure and then rapidly expanding the solution through a heated nozzle having a short orifice into a region of relatively low pressure. These processes suffer from the same problem in that they are only applicable to materials that are soluble in supercritical fluids and do not teach a process for patterned deposition. Moreover, the processes are not readily applied to curved surfaces, such as optical elements.
Components with curved surfaces are common-place in optical systems. Display applications that rely on a conversion of a flat, planar wave front to a curved surface, or vice versa, are difficult to implement because devices to convert planar to curved wave-fronts suffer from a number of problems. For example, fiber plates may induce a perceptible hexagonal pattern overlaid on the display and curved diffusive elements are difficult to manufacture without creating anomalies in the display. By placing optically active materials upon the curved surface of an optical element, these problems may be obviated. However, there is a problem in that no suitable technique for the deposition of the materials upon curved surfaces.
There is a need, therefore, for a patterned deposition technique that permits the patterned deposition materials onto curved surfaces or substrates. There is a further need for a technique for the patterned deposition of thermally unstable/labile materials that eliminates the use of expensive, and environmentally and human health-hazardous solvents, the need for post-deposition drying for solvent-elimination and is applicable for a wide range of functional materials and that is not limited by specific properties of the functional materials.
According to a feature of the present invention, a system for depositing a functional material on a receiver includes a chamber containing fluid in a compressed state. The fluid includes a solvent and suspension of the functional material to be deposited on the receiver. The chamber has a controllable nozzle for the ejection of a stream of the fluid toward the receiver. The system also includes a controllable platform for locating and orienting the receiver with respect to the controllable nozzle and a controller operably connected to the controllable nozzle and the controllable platform thereby controlling the ejection of the compressed fluid through the controllable nozzle and controlling the location of the receiver with respect to the controllable nozzle. The functional material becomes free of the solvent prior to the functional material contacting the receiver.
According to another feature of the present invention, a method of delivering a functional material to a receiver includes providing a chamber containing fluid in a compressed state, the fluid including a solvent and suspension of functional material to be deposited; providing a controllable nozzle integrated into the chamber for the ejection of the fluid in a stream; locating one of a receiver and the controllable nozzle with respect to the other of the receiver and the controllable nozzle such that the receiver is positioned to intersect the stream of functional material; and controllably ejecting the fluid through the nozzle, wherein the functional material becomes free of the solvent prior to contacting the receiver.